Re: [PATCH] x86/mm/pat: Fix L1TF stable backport for CPA

[Guenter Roeck]

On Sat, Aug 25, 2018 at 06:50:15AM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 
> Patch for stable only to fix boot resets caused by the L1TF patches.
> 
> Stable trees reverted the following patch
> 
> Revert "x86/mm/pat: Ensure cpa->pfn only contains page frame numbers"
> 
>     This reverts commit 87e2bd898d3a79a8c609f183180adac47879a2a4 which is
>     commit edc3b9129cecd0f0857112136f5b8b1bc1d45918 upstream.
> 
> but the L1TF patch backported here
> 
>    x86/mm/pat: Make set_memory_np() L1TF safe
> 
>     commit 958f79b9ee55dfaf00c8106ed1c22a2919e0028b upstream
> 
>     set_memory_np() is used to mark kernel mappings not present, but it has
>     it's own open coded mechanism which does not have the L1TF protection of
>     inverting the address bits.
> 
> assumed that cpa->pfn contains a PFN. With the above patch reverted
> it does not, which causes the PMD to be set to an incorrect address
> shifted by 12 bits, which can cause early boot reset on some
> systems, like an Apollo Lake embedded system.
> 
> Convert the address to a PFN before passing it to pmd_pfn()
> 
> Thanks to Bernhard for bisecting and testing.
> 

Thanks a lot to you for tracking it down, and sorry for messing it up.

> Cc: stable@xxxxxxxxxxxxxxx # 4.4 and 4.9

LGTM for v4.4.y but ... are you sure that this patch applies to v4.9.y ?
Commit edc3b9129cec is 'native' in v4.9.y and has not been reverted there.

$ git log --oneline v4.4..linux-4.9.y | grep "x86/mm/pat: Ensure cpa->pfn only contains page frame numbers"
edc3b9129cec x86/mm/pat: Ensure cpa->pfn only contains page frame numbers

Guenter

> Reported-by: Bernhard Kaindl <bernhard.kaindl@xxxxxxxxxxxxxxx>
> Tested-by: Bernhard Kaindl <bernhard.kaindl@xxxxxxxxxxxxxxx>
> Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/mm/pageattr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 27610c2d1821..1007fa80f5a6 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -1006,7 +1006,7 @@ static int populate_pmd(struct cpa_data *cpa,
>  
>  		pmd = pmd_offset(pud, start);
>  
> -		set_pmd(pmd, pmd_mkhuge(pfn_pmd(cpa->pfn,
> +		set_pmd(pmd, pmd_mkhuge(pfn_pmd(cpa->pfn >> PAGE_SHIFT,
>  					canon_pgprot(pmd_pgprot))));
>  
>  		start	  += PMD_SIZE;